PURPOSE: To evaluate the information assessed with the LADARWave wavefront measurement device and correlate it with visual symptoms, refraction, and corneal topography in previously LASIK-treated eyes.

MAIN OUTCOME MEASURES: Complete ophthalmologic examination, corneal topography, and wavefront measurements were performed. Correlations were made between the examinations and symptoms.

METHODS: Wavefront measurements were assessed with the LADARWave device. Manifest, cycloplegic refraction, and topographic data were compared with wavefront refraction and higher order aberrations. Visual symptoms were correlated to higher order aberrations in 3 different pupil sizes (5-mm, 7-mm, and scotopic pupil size). Pearson's correlation coefficient and generalized estimating equations were used for statistical analysis.

RESULTS: In post-LASIK eyes, wavefront refraction components were poorly correlated to manifest and cycloplegic components. The comparison between manifest, cycloplegic, and wavefront refraction with total amount of higher order aberrations showed no strong correlation. The comparison between topography and manifest, cycloplegic, and wavefront refraction did not show strong correlation. Visual symptoms analysis showed correlation of double vision with total coma and with horizontal coma for the 5-mm and 7-mm pupil size; correlation between starburst and total coma for the 7-mm pupil size; and correlation of double vision with horizontal coma, glare with spherical aberrations and with total aberrations, and starburst with spherical aberrations for the scotopic pupil size. Scotopic pupil size had a positive association with starburst and a negative association with double vision.

CONCLUSIONS: The LADARWave wavefront measurement device is a valuable diagnostic tool in measuring refractive error with ocular aberrations in post-LASIK eyes. A strong correlation between visual symptoms and ocular aberrations, such as monocular diplopia with coma and starburst and glare with spherical aberration, suggest this device is valuable in diagnosing symptomatic LASIK-induced aberrations. Horizontal coma was correlated with double vision, whereas vertical coma was not.

Last edited by Bill on Sat Oct 27, 2007 3:13 pm, edited 1 time in total.

METHODS: A prospective study was carried out involving 46 patients who underwent bilateral LASIK for myopia. Pupil sizes were measured before surgery using an infrared pupillometer under standardized settings. Pre- and postoperative refraction and best spectacle-corrected visual acuity (BSCVA) were registered. At the 3-month follow-up visit, the patients completed a questionnaire regarding night vision pre- and postoperatively.

RESULTS: The mean bilateral, spherical equivalent refraction (SE) was - 8.76 D (range 6.32 to - 12.0 D) preoperatively, and - 1.69 D (range 0 to - 4.38 D) postoperatively. The mean bilateral BSCVA was not changed by the operations. We found a significant correlation between large scotopic pupil sizes and the impression of worsened night vision (p < 0.01). A significant correlation between gender (males) and subjectively reduced night vision postoperatively was also found (p < 0.05).

CONCLUSION: Large pupil size measured preoperatively is correlated with an increased frequency of subjectively experienced post-LASIK visual disturbances during scotopic conditions. We recommend preoperative evaluation of pupil size in all patients prior to LASIK surgery.

Last edited by Bill on Sat Oct 27, 2007 3:15 pm, edited 1 time in total.

PURPOSE: To evaluate the effect of expanding the treatment zone of the Nidek EC-5000 laser on postoperative visual acuity as well as night glare and halos after laser in situ keratomileusis (LASIK) using 4 ablation zone diameters.

METHODS: This prospective study comprised 301 eyes of 154 consecutive patients who had LASIK in 1 or both eyes using the Nidek EC-5000 laser by 1 surgeon with experience in keratomileusis and excimer laser refractive surgery. A 6.5 mm optical zone was used with a transition zone 1.0 mm larger than the pupil under scotopic conditions (7.5, 8.0, 8.5, or 9.0 mm). Targeted correction was calculated according to a customized clinical nomogram. All patients were queried about glare and halos preoperatively and 3 months postoperatively using a questionnaire assigning numeric values to the degree of perceived visual disturbance (0 = no glare or halos, 1 = minimal, 2 = moderate, 3 = severe).

RESULTS: The baseline uncorrected visual acuity (UCVA) was 20/200 or worse in 293 eyes. The baseline best spectacle-corrected visual acuity was 20/20 or better. The mean preoperative refractive sphere was -6.33 diopters (D) +/- 2.80 (SD) (range -1.00 to -16.25 D) and the mean preoperative refractive cylinder, 0.86 +/- 0.83 D (range 0 to +3.25 D). Three months postoperatively, 78% of eyes had a UCVA of 20/20 and 99%, of 20/40 or better. Preoperatively, 94 eyes (31%) had glare and halos. At 3 months, glare, halos, or both were present in 19 eyes of 11 patients (6.3%) (P<.0001); in 14 eyes, patients reported less severe glare and halos postoperatively than preoperatively.

CONCLUSIONS: The use of a peripheral transition zone 1.0 mm larger than the pupil under scotopic conditions resulted in a low incidence of glare and halos postoperatively and did not adversely affect visual acuity. There was no increase in postoperative complications including corneal ectasia.

Last edited by Bill on Sat Oct 27, 2007 3:18 pm, edited 1 time in total.

Results
The effect of diluted aceclidine started about 15 minutes after instillation and lasted for about 5 hours. No difference between the 2 dilutions could be found. Thirty-nine of 40 treated eyes showed a reduction in night vision disturbance. The mean reduction in halos and double vision grading was 1.42 ? 0.5 (SD) and 1.14 ? 0.4, respectively. A mean decrease in pupil size of 2.5 mm was measured. Thirty minutes after the instillation of diluted aceclidine, the topography-derived wavefront error showed a statistically significant reduction in RMS values (total, spherical, astigmatic, coma, and higher order), which was maintained for 5 hours. A transitory conjunctival hyperemia was the only side effect reported.

Conclusion
Diluted aceclidine seemed to be an effective and safe treatment for night vision disturbance following refractive surgery.

"Glare is induced by rays of light that enter the pupil through the portion of the cornea outside the ablation area. A larger pupil allows more errant light rays to reach the retina and degrade the perceived image. For this reason, a larger ablation zone is required in patients with large pupils and high myopic corrections".

_________________Broken Eyes

"The price good men pay for indifference to public affairs is to be ruled by evil men." Plato

A 37-year-old ophthalmologist had bilateral simultaneous laser in situ keratomileusis (LASIK) for moderate myopia with astigmatism using the Alcon Summit LADARVision laser; an ablation zone of 5.5 mm was used. Five months after surgery, the uncorrected visual acuity was 20/20 and 20/25 but despite regular corneal topographies, the patient experienced prominent ghost images under photopic and scotopic conditions. To elucidate the nature of the problem, automated static perimetry was performed, which revealed a significant depression between 10 degrees and 30 degrees compared with a baseline study obtained 3 years earlier. The patient started brimonidine 0.2% 1 drop in both eyes every morning, which caused 1.5 to 2.0 mm of pupillary miosis (tonic pupil size 3.0 to 4.0 mm in dim light) and eradicated the ghost images. Repeat perimetry showed significant improvement in all indices. The mechanism of improvement is unclear but may be due to elimination of light scatter from the transition zone between the ablated and unablated cornea. The issue of perimetric changes after refractive surgery deserves more attention; postoperative testing may be indicated for patients in whom the ablation zone diameter is close to the mesopic or scotopic pupil size to provide an accurate lifetime baseline visual field.

_________________Broken Eyes

"The price good men pay for indifference to public affairs is to be ruled by evil men." Plato

METHODS: Twenty-seven myopic eyes of 19 patients were included. The mean preoperative spherical equivalent was -6.86 diopters (D) +/- 1.24 (SD) (range -4.25 to -9.5 D); the mean planned OZ diameter was 6.26 +/- 0.45 mm (range 5.7 to 7.1 mm). All patients had uneventful wavefront-guided LASIK (Zyoptix version 3.1, Bausch & Lomb) and an uncomplicated follow-up of 12 months. Wavefront measurements were performed with a Hartmann-Shack sensor in maximum mydriasis preoperatively and 12 months after LASIK. Wavefront errors were computed for pupil diameters (PDs) of 3.0, 3.5, 4.0, 5.0, 6.0, and 7.0 mm for the individual OZ diameter and for the individual mydriatic PD (7.93 +/- 0.46 mm). The impact of the relationship between pupil diameter and OZ diameter (fractional clearance [FC]) on HOA was described and quantified using curvilinear regression with a 4th-order polynomial fit.

RESULTS: There was a reproducible relationship between FC and the amount of induced HOA. The change in HOA root mean square and primary spherical aberration (Z(4)(0)) was significantly correlated with FC. If the OZ was 16.5% larger than the pupil (FC = 1.17), only half the amount of HOA was expected to be induced than if the OZ equaled the pupil. In contrast, an OZ that was 9% smaller than the pupil (FC = 0.91) resulted in an HOA induction 50% higher than at FC = 1.

CONCLUSION: The OZ zone to pupil ratio (fractional clearance) had a significant impact on HOA induction after wavefront-guided LASIK.

---------------------------------------------------
What about an OZ that is 25% smaller than the pupil???? That would be me!!!!

_________________Broken Eyes

"The price good men pay for indifference to public affairs is to be ruled by evil men." Plato

"There was a significant correlation between FC (fractional clearance) and HOA RMS..."

"The choice of the OZ diameter is a crucial step in excimer refractive surgery. Theoretical investigation showed that for a PRK of -5D, OZ diameters 1.5% smaller than PD (FC = 1.02) are at least required to prevent central glare by peripheral out-of-focus rays. In a recent study, it could be shown that induction of HOA after LASIK was significantly lower if the OZ overlapped the pupil (FC > 1). It is known that with increasing pupil aperture, the wavefront of the eye becomes more aberrated, and therefore a decrease of retinal image quality had been shown. Particularly spherical aberrations show a high dependence of PD."

"It seems eminent that both PD and OZ size have to be considered as factors of influence on post-LASIK retinal image quality."

"The 100% prevalence of induction of Z4 (spherical aberration) at FC = 1 is most likely the result of the effective OZ being smaller than its nominal value."

(that last excerpt refers to the fact that all effective optical zones are smaller than the programmed optical zone due to loss of laser efficiency as the laser strikes the slope of the cornea in the periphery).

"We found that if the OZ overlaps the pupil by 17% (FC = 1.17), only half of the amount of HOA is expected to be induced than if the OZ equaled the pupil. In contrast, if the pupil is 9% larger than the programmed OZ (FC = 0.91) the induction of HOA increased by 50%, as compared with FC = 1."

"Our theoretical study clearly showed that the higher the OZ to pupil ratio ("fractional clearance"), the higher the amount of induced HOA. This relation seemed -- for the population studied -- to be independent of the absolute HOA, pupil, and OZ size values. Results of recent studies of night-vision disturbances (ref Schallhorn and Pop) could be explained by this finding."

"So far, results from this study show that not PD itself but the ratio between the planned OZ and the scotopic pupil diameter (FC) should be considered before treatment".

"... OZ diameters that overlap the pupil by 15% or more could help minimize the difference between preoperative and postoperative HOA."

_________________Bill

"What concerns me is that if the person informing the patient is themselves poorly or inaccurately informed then how on earth can consent ever be truly informed?" Dr. Sarah Smith

We studied the effect of radial keratotomy on contrast sensitivity in 69 individuals with one eye operated and one eye unoperated in the Prospective Evaluation of Radial Keratotomy (PERK) Study, with a mean follow-up time of 13.8 months (range 6 months to 31 months). We tested contrast sensitivity under normal daylight conditions using both photographic plates and a computer-video apparatus. On average, we found no clinically meaningful loss of contrast sensitivity in eyes after radial keratotomy. However, eyes with radial keratotomy showed a statistically significant decrease in contrast sensitivity at the higher spatial frequencies of 12 and 18 cycles per degree, although all values were within the previously established normal range. Specifically, 44% of the patients had approximately the same contrast sensitivity in both eyes; 40% of the patients had 50% less contrast sensitivity in the operated eye than in the unoperated eye; 16% of the patients had 50% more contrast sensitivity in the operated eye than in the unoperated eye. Contrast sensitivity improved gradually in operated eyes between 6 months and 2 years after surgery. Eyes with radial keratotomy, in which the diameter of the pupil was the same size as or larger than the central clear zone, had slightly decreased contrast sensitivity compared to eyes in which the pupil was smaller than the clear zone.

_________________Broken Eyes

"The price good men pay for indifference to public affairs is to be ruled by evil men." Plato

PURPOSE: To determine whether the currently accepted method of selecting a minimum optical zone diameter for laser refractive surgery that is equal to or slightly greater than the dark-adapted pupil diameter provides a sufficient diameter of corneal surface to focus light arising from objects in the paracentral and peripheral visual field.

METHODS: An optical model of the anterior segment was developed to calculate the effective corneal refractive diameter (ECRD), which is the diameter of the area of cornea that refracts all incident light rays arising from an object through the physical pupil (PP). This model incorporates the patient variables of central anterior chamber depth (ACD), central corneal curvature (K(c)), and the diameter of the apparent entrance pupil (EP). The model was expanded to incorporate distant objects off the line of sight (LOS), described by their angular displacement from the fixation object in visual space (the object tangent angle delta(ob)). Results were calculated for the 360 meridian degree visual field (ie, for all objects in visual space perceptually displaced from the fixation object by angle delta(ob)). The effect of the prolate nature of the cornea was also investigated.

RESULTS: The ECRD expanded rapidly as a function of PP and delta(ob) but was minimally influenced by K(c). Beyond a critical object tangent angle delta(c), light rays striking the corneal vertex were not refracted through the PP, and the ECRD became an annular surface centered on the corneal vertex. The delta(c) was not a function of K, but increased as the PP increased and decreased as the ACD increased. The prolate nature of the cornea had little influence on the ECRD, even for very peripheral light rays.

CONCLUSIONS: The ECRD expands rapidly when considering distant objects only slightly displaced from the LOS. A patient treated with an optical zone equal to or slightly greater than the dark-adapted pupil diameter may experience vision quality loss for paracentral and midperipheral objects even under conditions of ambient indoor lighting.

_________________Broken Eyes

"The price good men pay for indifference to public affairs is to be ruled by evil men." Plato

Accurate scotopic preoperative pupillary measurements in both cataract and lasik surgery cases are critical to avoid in individuals with naturally briskly dilating pupils under scotopic conditions postoperative visual disability related to low light reflections, disabling illuminance, glare disability, halos, starbursts, and diplopia with night vision. Both edge reflections of the pseudophakos implant in cataract surgery and the ablated corneal margin in lasik surgery can contribute to serious visual disability in patients who have larger scotopic pupils exposing the edge of the implanted lens or the surgical optical zone of the ablated cornea to the entrance pupil. A case is presented in which cataract surgery was performed initially with a 5.5-mm-diameter optic lens in one eye and later a 7.0-mm-diameter optic lens in the other eye. Because of a naturally briskly dilating pupil of 7.0 mm, the eye with the smaller implant experienced significant night vision difficulties because of edge reflections of the exposed implant. The other eye in the very same patient with the larger lens implant was asymptomatic. This case underscores the importance of accurate preoperative pupillary measurements under scotopic conditions to avoid this preventable disabling surgical complication in both cataract and lasik cases.

_________________Broken Eyes

"The price good men pay for indifference to public affairs is to be ruled by evil men." Plato

We also found that the 6-month postoperativemesopic glaremeter value, but not the photopic glaremetervalue, correlated well with the subjective symptomscore, contrast sensitivity log value, and preoperativepupil size in both groups.

Quote:

Because enlargingthe ablation zone to match or exceed the mesopicpupil size can minimize induced aberrations,with the caveat being that larger zones produce deeperablations, a larger optical zone size may improve thesubjective symptoms and glaremeter values.In the present study, the preoperative pupil sizecorrelated with the postoperative subjective symptomscore and mesopic glaremeter value.

We feel that using the largest recorded pupil size rather than the mean of the 3 may give a better representation for the scotopic pupil. After all, it is the largest natural pupil size we are interested in and it is this pupil size that one should cover in planning for refractive surgery to avoid side effect like glare.

_________________Broken Eyes

"The price good men pay for indifference to public affairs is to be ruled by evil men." Plato

Who is online

Users browsing this forum: No registered users and 1 guest

You cannot post new topics in this forumYou cannot reply to topics in this forumYou cannot edit your posts in this forumYou cannot delete your posts in this forumYou cannot post attachments in this forum